High resolution 19F{1H} nuclear magnetic resonance spectroscopy and liquid chromatography–solid phase extraction–offline 1H nuclear magnetic resonance spectroscopy for conclusive detection and identification of cyanide in water samples

Abstract

We report herein a new, sensitive and efficient method for detection, identification and quantification of cyanide in water samples. Cyanide was converted (>95% yield) to its versatile and stable derivative, 1-cyano-2,2,2-trifluoro-1-phenylethyl acetate (CTPA).The crude reaction mixture was directly subjected to high resolution fluorine-19 nuclear magnetic resonance (19F{1H} NMR) spectroscopy. In order to do away with signal overlap and dynamic range problems associated with 1H NMR spectroscopy, liquid chromatography with UV detection hyphenated to online solid phase extraction (LC–UV–SPE) was performed. The trapped and enriched CTPA was thereafter subjected to offline 1H NMR spectroscopy. In this way the δ1H, δ19F spectral signatures and LC–UV retention time were used for specific detection and identification and quantification of cyanide. The three techniques (viz. LC–UV and LC–UV–SPE followed by offline 1H NMR and 19F{1H} NMR spectroscopy) demonstrated good linearity (r2>0.99), reproducibility (inter-day RSD: 1.43–1.89%, 2.60–2.80%, 1.42–1.60; intra-day: RSD 1.20–1.38%, 3.21–3.25%, 1.00–1.19%), accuracy (recoveries: 95.1–97.2%, 77.5–82.8%, 96.8–98.9%) and LODs (1.31μg/mL, 4.24μg/mL, and 2.14μg/mL) respectively. Total time required for the analysis was ∼3h. Utility of the method was demonstrated by the detection and identification of spiked water samples. Since the derivative CTPA was volatile, could also be analyzed by GC–MS and GC–FTIR instruments.